The developmental mechanisms by which diversification of function is achieved in the sensory systems of animals are poorly understood. The nematode C. elegans responds to multiple chemicals in its environment using a well-defined set of chemosensory neurons. We are defining the genetic pathways required for the functional specification of individual chemosensory neurons. The goal of this proposal is to fully describe the developmental cascade of events required for the development and function of the AWA olfactory neuron type. Our specific aims are three-fold: 1) To investigate the role of sns-1 0 and additional genes in AWA fate specification. sns-1 0. the C elegans ortholog of the homeobox gene aristaless plays a role in AWA neuronal development. The functions of sns-10 will be investigated, and its regulatory relationships with previously identified genes will be explored. Additional developmental genes will be identified in genetic screens using a strain expressing three different cell-specific fluorescent markers in AWA and lineally related neurons. 2) To analyze genes required for AWA sensory functions. The genes sns-1 and odr-7 regulate the expression of AWA-specific signaling genes. sns-1 will be cloned, and its role in the regulation of signal transduction genes will be studied. The functions of ODR-7-regulated signaling genes identified via microarray experiments will be examined in vivo. 3) To identify the mechanisms required for fate specification of the AWC olfactory neurons. An AWC olfactory neuron-like fate is the default developmental fate of the AWA and other chemosensory neurons. Over 300 mutants with defects in AWC-specific gene expression have been identified using a high throughput method. These mutants will be analyzed in order to explore the consequences of defects in AWC fate specification on the development of different sensory neurons. Investigating how the functions of individual chemosensory neurons are specified will allow for an understanding of how functional diversity is achieved in the sensory system, and will also yield insights into the fundamental processes of cellular diversification and development.